When shopping for LED light bulbs, sometimes the specifications for base type (E26 or E27) and bulb shape (A19) can get confusing.
Common screw in bulbs use a base called an Edison Screw or ES base. This base type was originally developed by Thomas Edison for the first ever light bulbs and is still in used today.
Below, we will discuss the four commonly used thread size groups for lamps:
- Candelabra: E12 in North America, E11 in Europe
- Intermediate: E17 in North America, E14 (Small ES, SES) in Europe
- Medium or Standard: E26 (MES) in North America, E27 (ES) in Europe
- Mogul: E39 North America, E40 (Goliath ES) in Europe
The number following the E indicates the size in mm of the external thread screw, thus a E26 has a 26 mm base diameter.
Sometimes, you can find low cost LED bulbs using an E27 base displayed third-party reseller sites such as eBay and Amazon from foreign suppliers. Even though these will technically work in E26 bases, its usually an indication that the bulb was not specifically designed for use in the US market and the bulb may lack proper North American, UL or ETL safety certification and therefore should be avoided.
Now that we have learned that E26 and E27 are terms used to describe the type of base used. What does A19 or bulbs with an A designation mean?
"A" type describes a bulb that has a pear-like shape. The number that follows the "A" within the A series indicates the width of the bulb in one-eighth inch units, or in millimeters.
The most commonly used A-series light bulb is the A19 bulb, which is 2 3/8 inches (60 mm) wide at its widest point and approximately 4 3/8 inches (110 mm) in length. This is the classic shape that most people are accustomed to when shopping for a "Light Bulb". You can utilize this image below to identify the size of your A Shaped bulb: